1. Technical Field
The present invention relates to a vibration actuator and an image capturing apparatus.
2. Related Art
U.S. Pat. No. 6,940,209 discloses a structure of a lead screw ultrasonic motor. This ultrasonic motor uses vibration of a vibrating body to move a threaded shaft back and forth in an axial direction. Japanese Patent Application Publication No. 2007-049897 discloses a tube ultrasonic motor. This ultrasonic motor includes an elastic body made of ceramic and has good abrasion resistance.
The ultrasonic motors disclosed above have an appropriate clearance between the vibrating body and the threaded shaft or rotating member. However, the settings for this clearance depend entirely on the precision of the dimensions of the components. Therefore, if there is dust or the like between the vibrating body and the threaded shaft, the vibration of the vibrating body cannot be smoothly transferred. In addition, manufacturing variations, environmental conditions, a difference in load, or the like may change the operational efficiency. Furthermore, material with good abrasion resistance, such as ceramic, is expensive and is difficult to process. Therefore, vibration actuators using such material are more expensive, and the range of possible uses is limited.